In the story of the woman caught in adultery, John indicates that the question of the Pharisees was a "trap".

2 At dawn he appeared again in the temple courts, where all the people
gathered around him, and he sat down to teach them. 3 The teachers of
the law and the Pharisees brought in a woman caught in adultery. They
made her stand before the group 4 and said to Jesus, “Teacher, this
woman was caught in the act of adultery. 5 In the Law Moses commanded
us to stone such women. Now what do you say?” 6 They were using this
question as a trap, in order to have a basis for accusing him.John 8:2-6 (NIV)

What specifically was the trap they were trying to get Jesus to fall into?

3 Answers
3

At this time in history Israel was under the rule of the Romans. The Jewish law required that a woman caught in adultery was to be stoned to death.

Leviticus 20:10 NIV

“‘If a man commits adultery with another man’s wife—with the wife of
his neighbor—both the adulterer and the adulteress are to be put to
death.

But under Roman law a person could only be put to death by the judge, otherwise it was murder. Much like our law today. Christ did not have the "authority" as a man under Roman law to sentence anybody to death.

Thus, if Christ had answered that the woman was to be stoned He would have be breaking the Roman law. Not only this, but the act of stoning this woman would have gone against the mercy, grace and forgiveness that He had been preaching about.

But if He answered to let the woman go, then He would not have been upholding the Jewish law. Christ himself had been teaching the people that whoever loves God will obey God. So to not Stone this woman would mean that Christ was not in obedience to God, which is also a sin.

Why didn't Jesus mention anything about the Roman Law when He resolved this adultery case? Seems like Jews were able to execute the stoning without any interference from the Roman soldiers.
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MawiaJan 20 '14 at 14:10

If Jesus tells them to carry out the law and stone her, he is not being merciful. If he shows mercy, he is construed to be disobeying the law God handed down in Leviticus. Whichever action he chose, in the Pharisees' minds, would enable them to accuse him of doing wrong.

They wanted to get Jesus in trouble with them (disregarding Moses' Law) or with the Roman government -- or both, if possible.

Adulterers were to be put to death, but the Law required two witnesses minimum to prosecute and convict before executing -- or at least two witnesses to cast the first stones (Deut 17:7). I'm not sure how easily the adultery was proven. Note that the man involved in the adultery was not recorded as being brought to Jesus, only the woman. It's possible that the law-professors set up the adultery situation themselves, laying a stumbling block in her path in order to lay a different one in Jesus' path.